Environmental Engineering Reference
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by 0.1 g -Fe 2 O 3 nanoparticles at 10, 22.5 and 35 o C was found to be 83.8%, 80.8% and
77.5%, respectively. Lower temperature favors Cr(VI) adsorption onto nanoparticles,
which is expected for physical adsorption. Adsorption capacity is determined by a
balance between the rates of adsorption and desorption. The desorption rate is
determined by the fraction of the adsorbed molecules at any given time which have
thermal energy greater than the adsorption energy. As temperature rises, the fraction of
molecules that can escape from the surface increases rapidly, and the amount adsorbed
decreases. The rate of adsorption also increases with increasing temperature but the
change is much less than for desorption (Needly and Isacoff, 1982).
30
25
20
15
Cu(II) pH=6.5
Ni(II) pH=8.5
Cr(VI) pH=2.5
10
5
0
0 0 0 0 0 0 0 0 0 0 0 0 0
Time (min)
Figure 9.14 Kinetic studies on the removal of Cr(VI), Cu(II) and Ni(II) (Hu et al., 2006).
100
90
80
70
60
50
10 ˆ
22.5 ˆ
35 ˆ
40
30
20
10
0
0
5
10
15
20
25
30
35
40
45
50
55
60
Time (min)
Figure 9.15 Effect of temperature on the removal of Cr(VI).
 
 
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